This invention relates generally to continuous porcelain enameling furnaces and more particularly, it relates to an improved porcelain enameling furnace which operates on an effective and efficient fuel basis. More specifically, the porcelain enamel furnace of this invention has a heat transfer section in which the incoming cool ware is parallel to and travels in the opposite direction to the outgoing hot ware, thereby permitting efficient heat transfer by radiation and convection to occur. The instant porcelain enameling furnace includes U-shaped radiant heating tubes in the heating section for facilitating uniformity of temperature from top to bottom of the porcelain enamel ware therein.
The present invention is generally directed to improvements made over U.S. Pat. No. 4,310,300 which issued on Jan. 12, 1982 and is entitled "Furnace for Porcelain Enameling". Such patent is hereby incorporated by reference. Due to the particular configuration of the present furnace, the outside wall area is reduced for the same conveyor length and production capacity as the furnace in the '300 patent, thereby permitting a more compact layout. Further, this design configuration includes a heat transfer section in which the incoming cooling ware and the outgoing hot ware are arranged in a side-by-side or parallel relationship to provide efficient heat transfer therebetween.
In the above patent, gases from a burner combust in a plurality of serpentine radient tube units in the heating zone which are disposed on opposite sides of the furnace. Then, the products of combustion from the radiant tube units are collected by a pair of manifold pipes arranged on the inside of the heating zone. This suffers from the disadvantage of being inefficient in releasing an appreciable amount of heat since the manifold pipes are inside of the heating zone. On the other hand, the present furnace is provided with U-shaped radiant heating tubes which extend vertically downward adjacent the outside wall, horizontally across the floor, and vertically up adjacent the inside wall so as to effect an even distribution of heat within the heating section.
Further, the products of combustion are collected in an external exhaust collector duct for delivery to U-shaped hear exchanger tubes formed in the pre-heating section. The external exhaust collector duct is preferable refractory lined and serves to replace the internal manifold pipes of the '300 patent which are made of an expensive alloy, thereby reducing the maintenance and replacement costs. The products of combustion may then be passed through an external preheat collector duct to either a frit dryer oven or a heat transfer device via a hot fan and an insulated dryer duct. As a result, most of the thermal energy in the combustion product has been utilized or reclaimed to facilitate an initial heating of the cool ware. Thus, the temperature of the spent exhaust gases to be vented from the dryer oven into the atmosphere will be at a relatively low temperature such as approximately 200.degree.-300.degree. F.